Neurons that respond to faces show stable behavior even as the brain changes.

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The human brain is composed of approximately 100 billion neurons, each with distinct functions. One of those functions is face perception—the ability to recognize what someone looks like and recall who they are. The ability to recognize faces persists for years, even though the brain is also plastic, constantly rewiring its connections. This raises a question: do the neurons responsible for face perception change due to this constant rewiring?

A team of scientists from the National Institute of Health may have an answer. They located the brain regions where face-specific neurons resided by recording activity using functional MRI (fMRI) while showing macaque monkeys images with and without faces on them. Microwire electrode arrays (tens of tiny electrodes) were then implanted into these brain regions to provide detailed records of the activity of neurons.

Initial recordings were made after implantation to obtain a baseline record of how the neurons responded to different images. This helped to isolate neurons that were responsive to faces (and to validate that the implanted electrodes actually worked). Over the course of a few weeks, the scientists then showed the monkeys a library of images—some with faces and some without—and investigated the consistency of neural responses over time.

In their analysis, the scientists used waveform shape, frequency (the number of spikes occurring within a second), and consistency to assess changes in the response of the face-specific neurons.

The results showed that face-specific neurons respond to images with faces in the same way over long periods of time—in one case, recordings went for a year. In addition, the same neurons repeatedly respond to the same faces, suggesting a sort of association or mapping: certain faces always triggered certain neurons. This suggests that the brain's ongoing rewiring process doesn't significantly affect them, and thus may not have a large impact on recognition of faces.